Help please

Hi guys, I have a question, im having trouble believing my boyfriend isn't gay or bisexual. I'm not sure what to do, we've had fights and arguments about me believing he is gay or at least bisexual, but he'll get really defensive and say he's not and stick with it, but then it'll be brought up again bc of me I'll feel like something is fishy and odd. Is it odd that a guy from the gym, messages him saying he's handsome and calls him sexy, but he doesn't reply to that, he ignores the fact that he is saying comments like that. Last night my boyfriend asked me randomly if I thought that dude was gay when he showed me the messages from him getting called "I see your sexy ass" when he arrived to the gym. The dude messages him saying he's handsome, and posted a sc of my bf at the gym sitting down caught off guard but the caption said "training with him, ❤️😍" my bf tells me they talk about his ex and me at the gym, but I find it so hard to believe that something isn't going on. My boyfriend has told me that gay guys have come up to him and tried hitting on him. I'm just confused, he says repeatedly he's not gay or bisexual and that he's sure about himself, but I doubt myself and him. I've come to a point in our relationship where I feel insecure about guys and women and i shouldn't have to feel like that. It's been 7 months with my boyfriend and for the last 2 months he's been acting different and treating me less than what I treat him. He's offended me bc we stopped having sexual inter course bc I didn't like the way he wasn't treating me and wanting him to earn it back and treat me how he did when we first met. I just need help realizing signs if he's bisexual or gay, or if he's afraid to come out, like I know it's not my place to tell him or force him to tell me but I'm in a relationship with him, and I don't want to be feeling like I have to worry about men and women, and I don't want to be betrayed or used as an experiment. Whenever I tell him like I'll never judge just to be honest, he gets mad and then we get in a fight again. I just don't know what to do, he leaves to UC in 10 days, and we've been fighting so so much about nonsense, when I ask him to break up with me, he says no and never wants to. I just feel like he lost feelings for me, and especially now that he's going away. He says he wants to make it work when he leaves and that he wouldn't be here still if he didn't want to. I'm just confused and don't know what to do. He makes me happy and I love him, but I just been feeling insecure and not worthy at all. We see each other almost everyday literally. He's my best friend, and I told him as a friend I would still never care if he was or not. And he just stayed quiet. Like I don't know, hopefully someone can help me, I know this post is long and maybe no one will reply but I just need to vent out. Sorry guys, maybe it's me and not him. Blehhhh