SD usually has the most issues (likely psych disorder inherited from BM.) She is also here almost all the time. Those two factors add up to more correction. Then there's my oldest son who is unmotivated (just found out he's getting a D in science- not applying himself- this is a straight A student who's teacher told me last year should get a full ride to college.)
Then...there's my 10 year old. If you look at him crossways his eyes widen or tear up. You tell him, "I can't believe you disrespected me that way," and he corrects himself instantly, remorsefully.

So SD and DS (both around 13) complain that he's "the favorite" b/c we compliment him whenever he's thoughtful or self motivated. For instance this weekend he did his booktalk (book report presentation) all weekend long. Worked HARD on it for several hours. It isn't due til Tue.

So we compliment him and the other two look at each other and collectively roll their eyes in solidarity. We compliment them too, mind you, but...they don't do things as often worthy of complimenting. Or... they do them JUST to be complimented whereas 10 yr old is self motivated to try to do things for others.

As I told SD recently when she whined, "You guys make us (her and my older son) feel like he's (10 yr old) is perfect." I told her, "I don't. I correct him too. He just gets it right away so I rarely have to re-correct him 10 more times for the same thing. I refuse to apologize for complimenting him and encouraging him to continue this behavior. He works hard for it. If you and (older son) would pay attention to how he gets the compliments and work toward behaving in a way that inspires us to compliment you..." etc etc etc- falls on deaf ears.

At my exH's... it's more like your situation. Exh and sons' SM argue about each other having different standards for their own kids.

Then you add in your situation SK's mom dying. That's a whole other level. He's trying to make up for their loss. I can't imagine the position you're in. I would say sit down with your BF and have a sincere conversation. If he gets defensive try this line....

"I didn't say you were doing these things to intentionally make me feel this way. I am not saying you are responsible for my feelings. I am just trying to talk to you about my feelings. If I can't communicate my feelings to you, then we don't have a good relationship." Say it very CALMLY. This is turning emotional feelings into logical thought (since you take responsibility for them.) I have found that my DH only understands my feelings when I explain them this way. Men want to fix things/ us. If they don't know how, then they tend to get defensive that it's not their problem. If you absolve him from fixing it, but let him know you need his help working through it, he should relax and try to help.

If not then you need to do some serious thinking about your relationship.

Peace, love, and red wine