Not being mean, but your life is about to become much less peaceful.

How often is SD with you guys? Is there a way to compromise and accomodate both wants? Maybe a smaller trampoline? Maybe one of those in-ground trampolines so it's not such an eyesore and takes up less space. 

Is there yard space on either side of the house or the front yard that could accommodate your gardening needs? Can you plant some of your garden vertically? My parents have a smaller yard so they stacked pots on a metal post and planted all their herbs and small veggies like that. It looks beautiful because its different and artsy. Can you get creative and do some research so you can have the garden you want in a smaller space while still accommodating a smaller trampoline? 

Yes, the kid wants a trampoline. Why does she not have one at Mom's house? Could there be insurance reasons?  Check your home owners insurance. Some companies do not cover them. Others cover them only if they are set up a certain way. You'll definitely need an increased home owner insurance. 
Check the local zoning rules. Does a trampoline require a fence of a certain height around the back yard? Some areas consider a trampoline an attractive nuisance.

Has boyfriend/dad read what pediatricians say about backyard trampolines? https://www.healthychildren.org/English/safety-prevention/at-play/Pages/...

BF needs to learn not to put the onus on you. Telling her that it was up to you is unacceptable. If this continues, you'll be viewed as the evil stepmother as there is no way you are going to be able to say no to the wants that are to come if you give in on this one.

"No." Is a complete conversation.

And.... your BF is a coward throwing  you under the bus like that.

Good luck with this shit show.  In all liklihood it will not get better from here. The tramp is merely the first shot across the bow.

If it were me, the answer to the trampoline request would be a firm "NO!"  You have already sacrificed having a house with large garden so that you can be near the SD.  Like you, my garden is my mental health.  I would not be having any entitled step child deny me that. 

Wow he threw you under the bus quickly. You need to have a serious conversation with SO about rules and expectations. He needs to parent his daughter, especially since she is a pre-teen. He doesn't ever get to say, "it's up to Tstar." That makes you the bad guy. It should be a simple, i'll think about it and get back to you. 

Not to mention, I'm guessing SO knew about your plans for a garden. Since it is so important to you, I'm guessing it was a consideration and discussion in what house to buy. If so, really a red flag. He's already sacrificing your space to make SD happy. 

Isn't 12 a little to old for a trampoline anyway? 

This does not bode well. Your "great guy" BF is already abdicating his parental responsibilities and being a crap partner by saying "it's up to Tstar."

Your response is to reinforce your role in the child's life:  BF,  that's a parental decision, and I'm not her parent. You know a garden is important to me and I'm not going to give up what little space I have for that, so let's discuss what's realistic.

Be on guard for him stomping all over your boundaries so that he's not the one to upset the precious child upset. He'd be very happy for you to be the bad guy.

Ask your BF why he abdicated a parenting duty to you? And is this going to be the norm going forward? Is he going to leave decisions that pertain to his daughter and her safety to you?

See already your path is being created. The first question your SD asked your BF made you the bad guy, fall guy, bad cop, scapegoat.

More to come lady ..

Say no since your BF left this up to you. No need to talk about it.

Man I feel for ya. Its gonna be a rough ride. You have never had kids and you step into a world with a pre teen SD. 

Gawd. Your peaceful garden will turn into a grow op. You'll need it

The daughter and mom live even on the same street?? Oh Lord no. I wish you the best. After 47 years you have likely entered into a miserable phase. Being single isn't nearly as sad and or lonely as this will quite possibly be. Best of luck.

Your BF needs to come up with some reason she can't have a trampoline (insurance, etc.) that has nothing to do with you. And then he needs to grow a brain and/or a backbone and learn to say "I'll have to think about that" before he responds to requests like that. Not "I have to ask tstar" or "It's up to tstar."  He needs to learn to buy time so he can discuss things with you without you being the bad guy.

As for the trampoline, IMO the answer should be no. Tiny yards are not a place for large play structures. It's not fair to everyone else to use the entire yard for the trampoline. You are a full time resident whose wants trump those of a 12 year old.

How often is this kid with her father? I would be very cautious about this situation, as your BF failed his first test. Did you buy this house together?

Step 1:

"SD, your dad and I need to discuss this first, okay?" Say it with a smile to SD.

Step 2:

Pull your SO into a private space and tell him:

"SO, in the future, you and I need to discuss these items first and not just have me be the one to give an answer. That can make me the bad guy if I say. And in this instance, I want to say no because <insert all reasons why you want to say no and any concerns you have about SD not using the trampoline, getting hurt on your property, increase in homeowner's insurance, etc>. We should be a united front when it comes to making decisions, and you should be the one to deliver those decisions to SD as her father."

If he tries to argue, even in a "oh but dear, I want you to feel you have authority...", say: "SO, I appreciate your feedback, but this was not something that is up for debate. If you put me in this situation again, I'll handle it the same way again. I will not be the one to give her answers solely for things that should be joint decisions."

Step 3:

Repeat Steps 1 and 2 as necessary.

IF you really want to make SD comfortable at the home and want to be able to incorporate her in the backyard somehow, talk to your SO about offering something else to SD for the backyard. At 12, she'll care about a trampoline for approximately 5 minutes before she's completely outgrown it. However, helping her bring something more grown up into the backyard that is peaceful (chair swings, fire pit, hot tub, lounging area with giant pillows) might be a great compromise.

If your SO isn't an arse, he'll agree that this is a good compromise. After he tells her no to the trampoline, you two can ask her what *relaxing* activities or things can be incorporated into the backyard. Offer her some ideas. Express how it will be usable over time. Talk about how she can have frienda over, etc. You get the idea.

There is a win-win in this situation, I think, if everyone bends a little. A trampoline is bending a lot, so stick to saying no.

My DH bought a trampoline for my YSD15 for her birthday in February. She uses it maybe, maybe about an hour a week when she's here. And we've had great weather.

I did not agree. She was too old. It's a novelty. Our homeowners insurance allowed it with strict guidelines. In a small yard it may not be allowed, and you could risk losing your homeowners insurance if you get one anyway.

A kids want like this does not get to take over the adult space.

Your SO did this you under the bus here, including moving close to the BM. Is he willing to stick to a visitation schedule or is she just going to show up and leave whenever?

You need to have a think about your boundaries as the childless adult and make sure your SO is clear about them as well.

At 47, I would not be putting up with this BS. Never would I ever live so close to BM. So you "had" to live in a certain area so that is was walkable for SD? Are her parents too bothered to arrange pick ups/drop offs? Sounds like your BF is too bothered by anything.

Nope! My advise would to let your bf keep doing all his responsibilities to his daughter. It's a lot easier if you don't start doing things that he normally does. Focus on being his partner and only help when needed as you please. Don't let them push you into an unpaid nanny role. This is what I learned from the seasoned members when I first read this forum almost 10 years ago. 
 

I also don't do any scheduling him and the mom do it all but I do want to be consulted if it will affect me. 

I'd suggest you volunteer him to buy a trampoline for the mom's house as your yard is too small. 

I've been in stephell for a very long time. You're making a terrible mistake. I feel a headache coming on just thinking about what's in store for you.

please dont be frightened off by all the responses we give.   However , you were certainly used by your BF as the scapegoat as he didnt want to be the bad guy and say no!   This will quickly become the norm if you dont put your foot down firmly.  It made me shudder when you said you all moved to be closer to the BM's house so the skid can walk back and forth,,, just wait , this will become hell in itself when the skid starts dictating that she can go back and forth as she pleases leaving you with no consistant visitation schedule, leaving your life to be scheduled around someone elses kid,, its wears thin very quickly