How do I ever trust another man?

Genuine question! I am a single mum. My two eldest are from a destructive 6 year relationship and my youngest is from a guy who walked out when the baby was 3 months old after promising me the world. I am an attractive woman and I have had plenty of offers but I turn down perfrectly good men as I daren't take the chance. My sons are my life and I ensure they have a relationship with their father(s) but it really shook my beliefs and trust in men when a man I thought I would marry found it so easy to leave. Of course there was another woman involved (from the office no less, how cliche!). I now realise I am well rid of him but how can you trust your feelings when you were once so gullible? I cant have men in and out of my sons' life either but I'm lonely!! Oh what do I do!!!!