1. Have your own life. Remember what you were like when you and your boyfriend first met? You had friends, hobbies, and lots of things that were not centered around him. Make sure you're still keeping up with those things. Doing so will make you happier, more interesting to him, and less likely to fixate entirely on your relationship. In Love? Don't Forget Your Friends
2. Schedule things out. Having a weekly date night, a monthly day trip, or regular evening text session on both your schedules can give you the sense that things are less amorphous and provide both of you with something to look forward to.
3. Tame those "what if?" demons. Stop thinking "what if?" every time you're apart (What if he sees a prettier girl while he's at the bar with his friends? What if he's not calling because he's on the phone with his ex? What if, what if, what if). Whenever your anxious thoughts start to spin out of control, remember that "what if?" is a lot less important than WHAT IS. And then remind yourself of what the reality of your relationship is.
4. Remember that you're great. You're beautiful. You're smart. You're fun. If you weren't, then he wouldn't have started dating you in the first place. Remind yourself from time-to-time of just how amazing you are. Regardless of whether you're in a relationship or not, it will make you feel more secure and centered.
5. Tell him outright. If the reason you're acting clingy is because he's treating you like you don't matter, then it's time for a talk. It may be the case that he doesn't realize how he's making you feel. It may be that he's just not into you anymore. Tell him, and if he refuses to work on making things better, get out. He "Has A Lot Going On." What Does That Mean?