There are meals when all I eat is cantaloupe with cottage cheese. I look at it as fruit, dairy & protein all wrapped up in one dish & I need quick & easy most of the time or I won't eat at all, so that's better than not eating.
IMO, PB & J is good. You are getting bread/starch....PB is wonderful protein, & J even though it's got a lot of sugar, you do get some fruit.
Eating alone is never easy & cooking for one person is the most difficult thing I do.
The one thing I do love is my BBQ which I hadn't used much this summer but it's so easy to just throw a steak on or a slab of salmon onto the gas grill & poof, it's done in no time & adds a great flavor. Though the other night when I was BBQing my salmon I ran out of the propane. Luckily it was right at the end & my Salmon was finished being cooked.
I understand your struggle when eating alone though & many times when I've been working out in the yard, I'm just too tired to even want to think about cooking. If I don't have a quick salad to throw together or something easy, I just don't bother eating & that is really a lot less healthy than PB & J.
Be happy that you are eating even that during the difficult times rather than turning to not eating at all.