As a female who married her second boyfriend. Men who delay marriage to play around will have less choice. Many of us are not searching for men to marry when we are 30 or 35 or even 26. We already are married, or know who we are going to marry.
There are so many married men out there who try to chat to us at races and just slightly push the boundary of what is appropriate. Its very tedious. They will try all sorts of tactics, offering ride shares to competitions, trying to "advise" you how to train, hanging around the finish line to check in on you and chat about your performance, which then extends into your race, contacting you on social media "to chat". Of course theres also married men who want affairs, who are even worse. All with a similar story to the OP.
Can I also say that there are a number of married men who choose the homely woman deliberately? The one who isn't their soulmate, or great love, or whatever. They do that to have a peaceful life or avoid competition from other men. The married men trying to do the chatting to us at races are ALWAYS in this category. They never seem to be able to marry a female runner, or a woman who shares their hobby, even when there many women who do that hobby. Increasingly, I see men at races with girlfriends from the far east (its never Germany, or Sweden, or France or similar) and they can barely communicate because the woman hardly speaks English, yet she hang around like a little dutiful maidservant. These are the worst men by far for trying the extra-curricular contact I describe above.
My advice to the OP is to date women who share your interests and values, who have a similar level of education to you and a similar background. You're more likely to form a strong connection with them based on shared interests and background than with random strangers. Your kids will then be less likely to grow up in a single parent family too.