Why is it so difficult to meet love? I just don't understand it and am suffering from this. Please advise me?

I'm a woman of 48 who thankfully looks and feels about 33. This is due to keeping active and eating well. I've had a good career and lots of lovely friends. My only heartache is that is seems so difficult to have a relationship which works and lasts. Sure I've had two serious boyfriends, one for a year and a half who wanted to marry but I wasn't into him enough to settle. The second was 14 years younger and ended the relationship after 4 years as he couldn't commit for a life. I am a good person and would love to meet someone with whom it works. I've tried dance cles, travelling and even internet dating clubs all to no avail. I usually go about my day without focussing on this as I tend to take it in my stride. This helped by the fact that I often get asked out and do feel attractive. The problem is that I'm only really attracted to much younger guys. I don't want a guy who has children. However, after the most recent breakup with a guy of 24 (we dated for 2 months) I feel that it is so hopeless. This hurt me a bit as I liked him so much even though he had a serious drink problem and knew it couldn't continue. I started saying to myself 'am I a ?', it was that bad! I know I'm not a of course but why is it so difficult? Thanks for any advice.