I split up with my wife about 35 years ago and got into another relationship quickly.
However with two children involved, and all the hassle of a divorce, and finding a new place to live, I found it hard to get too committed to this new partner.
Our relationship was on and off for many months (she would live with me for a while, then move back to her parents, then come back to live with me).
In the end she fell pregnant after we had been seeing each other for about 4 years and we got married.
So it was about 4 years between me meeting her and getting married (we are still together after 28 years of marriage).
However don't underestimate how difficult it is to split up from your husband / wife, and how much it affects you life. For a long time you feel a failure and are scared to get too deep into another relationship.
You have only been seeing this guy for about 3 months or so, which is nothing really, so you should not even be THINKING about your long term future, just enjoying your time with him..
I have to say if you start putting too much pressure on him you will drive him away.
So back off from the pressure, make life with him FUN, try to make him forget his failed marriage, and maybe when all the divorce etc. is over he may think about settling down again.
But it may take him a couple of years.