Just needing to vent

Just needing to rant…i met this guy 15 years ago, we ended up getting married and having two kids together…after we had our second he decided he didnt want to have a family anymore…since then he has always paid child support but NEVER seen or contacted them no matter how open i left the line of communication for him…my kids are 12 and 14 now and i even went as far as sending their numbers to his mom to send to him if he wanted to reach out…and nothing…i was always honest with m,y kids but i feel so bad for them because i feel like they are missing out on knowing their “real dad” and his entire family…hwo can you go through life knowing you have kids and wanting nothing to do with them? this will never make sense to me