10 Year Age Gap PLS Help!!

Hi everybody I usually don't post or ask for advice, but I need to. I am dating a 28m and I am 18f. We were coworkers but aren't anymore. Things are getting super serious for me, but he has a girlfriend and I don't know how he really feels about me. First let me explain how we started. I began being friends with his girlfriend and at this time I was 17. I ended up meeting 28m through her because they are boyfriend and girlfriend for a couple years. I started to work with him about 5 months after meeting his girlfriend and I really started to like him. I don't really like his girlfriend that much because she can be a real pain and also just talks down on me its super annoying. Anyways me and 28m started hanging out outside of work and I started catching feelings and I know he did too because he was spending a lot of money on me. Mind you I am still 17 at this time!! He bought me hundreds of dollars worth of food when we went out on dates every week and he would buy me random little gifts and give me rides. He tried to kiss me but I shoved him off since the age gap and I was a minor. We keep dating and after I am 18 we eventually kiss, hook up, and make love to each other. I am so head over heels for this man, but I feel like it is so wrong to be with him. Should I find someone my age? He lives with his girlfriend and they both are out of love, I know it is a convenience thing that they are both trying to save money and it is easier to live together. Also I wouldnt want him to break up with her because I dont know if I should entertain this thought of marrying and having his kids. Im sorry this post is crazy and messy but I am totally lost of what to do. Anything helps, thank you guys.