DH and I are both...selective...eaters. I'll admit I'm not a really adventurous person, but he is far worse than me. He did eat with his family but only the bare minimum to stop the nagging and really in the end they just knew he would fend for himself...enter PB and Marmite sandwiches. For school lunches, he took sandwiches. Dinner was sandwiches. If he even felt one stab of hunger, sandwiches. It's just how he is. To this day even. He got more adventurous in his 20's when colleagues at work coaxed him into trying new things like curry which led to him then trying more spicy food like chili. But that was it.
When I met him at 28, I started introducing him to other things, salads, fajitas, pasta dishes, meat on the grill, stuff like that. He is actually a decent eater now. But he does still have that phobia and will not try new things very easily. He will in fact really get upset and angry if you try to coax him at all. So the best thing for him, as with kids it seems, is exposure. I cook something, put it on his plate and he'll eat it. He might not like it very much (like sweet potatoes for example) but he'll now eat it to model for Finn. Last week I got him to put spinach in his lunch wraps. He loves it now!