In love

My boyfriend and I started dating/talking to each other in late June or July but I broke it off mid September because he was getting too close and it freaked me out. He was very persistent in wanting to be with me and not giving up so we got back together like 3 weeks ago. In the middle of sex he told me he loves me and I couldn’t bring myself to say it back. I know he means it because he says it a lot now but I’m not sure I know what loving another person is supposed to feel like. He’s my first real relationship! So how do you know if you are in love?