If he truly lives his life today based on his past (regarding the two failed marriages), you may not be able to change his mind. He has to work on himself, resolve the past which is keeping him stuck and be willing to take chances and offer you some sort of stability and long term commitment.
A man can have female acquaintances and you have got to make sure he is not trying to socialize with other women in order to fulfill some sort of a void that he has within himself. He may be doing it subconsciously thinking that being friends is the safest thing to do. No involvement, no break ups, no legalities, etc. If this woman is single, she may be too trying to avoid something in her life and the two of them can become codependent to each other. It would be a different scenario if let's say she was married and he was getting together with both her and her husband. Single uncommitted men may have another agenda when trying to befriend women. But, to give him the benefit of the doubt, perhaps this is how he wants to live for the rest of his life- not committing seriously to one specific person, or even if you are the love of his life, he is not emotionally involved 100% percent.
What you do will depend on what sort of life you would like have for the next 3+ years. Do you want to be hopeful that he will change his mind and you and him can commit to one another legally (getting married), would you be OK if you never get married but remain lovers and honest to one another, think about what is it that you want out of life at this stage in your life and if his desires for the time being and then the future are compatible.
You will have to look at this situation objectively and it may present you with things that you do not per se want to see. In order to be able to feel all right about whatever it is you decide to do, you've got to at least be honest with yourself asking and answering this to yourself- is this enough what I am getting out of this relationship, s he willing and able to give me more, what time frame should I allow him to see if he changes and what time frame will be enough for me to move on if needed.