Boyfriend can’t say “I love you” back

So I would consider myself a pretty understanding person. My bf has gone through a lot and has trauma from his childhood and apparently has only said “I love you” to his mom. He doesn’t even say it to his dad who he sees pretty often. He doesn’t feel comfortable saying it. We have been dating almost 7 months, and I have told him I love him a couple times, and he said he does love me too, without saying I love you. He will say “I do.” If I ask if he does. But today when I said I love you, he doesn’t say it back. He just says, thank you, you’re important to me. I can’t help but feel a little bit hurt. I know he has a very hard time sharing emotion and being vulnerable, but I’m his girlfriend. He should be able to be vulnerable with me. I tell him he can tell me anything. He has a hard time sharing emotions but I reassure him. I suggested therapy, he doesn’t want to go. I also have trauma from childhood and I have found therapy helpful. Idk. If we end up getting married one day, I want to be able to feel like my husband can trust me completely , including emotionally. Thoughts ? Not sure how to approach this. Thank you in advanced.