1. 1. As the property is in joint Names each of you would have to prove your share of contribution towards the flat and accordingly in that ratio the value can be distributed and one can buy the others Share accordingly should your husband be traced out .
2. 2. I have a doubt I am unable to understand as to his where abouts can be know if you contact his in laws his relatives etc and in this manner things can even be sorted out by seeking Mutual consent Divorce if he agrees which gets over within a 6 months period .
3. 3. Alternatively like most women sensitive Sympathetic lawyers advise you can file a case Domestic violence and seek Right to residence and stay forever and ever in the Flat and seek an exparte order from the court as your husband is not traceable. But this ex-parte order can be challenged at a later date .
4. 4. In your query it has been stated that you want to move on in life hence we have to presume that you are having an affair and hence wish to remarry . Now should your husband pop up at the flat at any moment and you are caught with your boyfriend ♥♥♥♥♥ whom you wish to Remarry in the absence of any Divorce decree in hand the circumstances would be Dangerous and the two of you ( you and your boyfriend ) would be in deep trouble. Since he can file a case against your boyfriend /Lover and would call in witness as your neighbours . ☺☺☺
5. 5. In Your post you have stated that you do not want anything $$$$$$$$ , even if you wanted anything (Maintenance) for yourself the court would not grant the same to you as I can observe that you are a working women self sufficient capable of maintaining yourself for the past several years , except for your son the two of you would have to contribute till your child turns into a Major upto the age of 18 yrs.
6. 6. You seek custody of your son the same can be granted and so can visitation be granted to your husband should he seek the same while contesting the case or challenging the exparte order .