It would have helped to know how long you’ve been dating this guy! 🙁 If you’ve been with him for a year or more, then you would realize that he’s got this pattern and it doesn’t mean there’s something wrong — he just can’t multi-task. If it’s only a couple of months you’ve been dating then I’d be concerned that the two of you are on the same page in terms of commitment in the relationship. Sometimes when one person isn’t sure if they’re dating The One, they date the field until they are sure. If you’re not hearing from him after only four or five dates with him because he’s dating other women, then I’d advise you to cool things down in your own heart and stay busy.
But if this is who he is, then you have to accept him for who he is and remember the good things about him that keep you in the game. For instance if your boyfriend was a terrible dancer — genetically terrible and not the kind of klutzy that can be helped with dance lessons — then I’d advise you to not go dancing every week, and instead find other things to do like hiking, dinner, movies, etc.
If your boyfriend is a great, committed guy, but gets busy in, say, trial if he’s a lawyer, or heated business deals if he’s an entrepreneur, etc., you have to find a way to get through these times by staying busy and expanding your own life even if it means taking up a new hobby or exercise routine, and also understanding that you are different from him, and he does things differently than you do, but it doesn’t mean there’s trouble in paradise.
I hope that helps. Your insecurity can be cured by understanding and compromise as well as seeing the ultimate big picture result — that you have a great relationship with this guy, but neither one of you are perfect, and he goes underground periodically, while you get a little anxious, but you both deal with your incompatibilities that are not deal breakers in this case, and come out no worse for the wear.