I'm sure you do feel guilty, but suicide isn't the answer is it!!!
You have to learn to live with the things that you do in life, and sometimes those things are bad. Ask yourself who you will hurt the most by either telling your husband or killing yourself? Your husband doesn't know anything, and I presume that he just thinks that you're a loving wife. If your son senses any hostility towards him, 4 months of age, it would barely register. You shouldn't hike your child, it's not his fault. I assume that your husband loves you his son, because make no mistake, while biologically he may be someone else's, he will grow up in a family with a daddy who loves him, unless you do something stupid to salve your own conscience. I can imagine that your husband looks upon his son with pride and satisfaction, because I know how important male children are within Indian culture. Think for a moment what it would do to him to learn that the child is not his. Think what it would do to the child. If you tell anybody, you will destroy your family, you will destroy yourself, and everybody around you will suffer. If you kill yourself, the outcome will be the same. Everybody will be hurt, except you, because you will be beyond pain. Suicide is the ultimate act of selfishness unless it is self-sacrifice to save others. You do not come into the 2nd category, you would be committing an even worse act of betrayal by killing yourself.
If I sound unsympathetic, I don't mean to. You have to learn to accept that we all make mistakes in life, it's what we do about them that matters. If you value your marriage and your family, you will stop seeing this guy. You know that sooner or later, if you continued, you will get caught, and once again, devastation will be the result. So you have to stop seeing this guy, And for gods sake don't tell him that he is the father of your 4 month old boy. That would give him some kind of hold on you, and you really don't want, believe me, you really don't.
You have 2 come to terms with what you have done, and learn to accept that you can't change anything you have done already, but you can change your happens in the future. But before anything else, you have to understand that until you forgive yourself, you won't have any peace of mind. In truth, everybody makes mistakes, and 99 times out of a hundred, and mistakes don't come back to haunt us. Your mistake created a child who needs your love and attention, and a strong family to grow up and be happy. If you can forgive yourself, there is really all you need to do. No one else is aware of what you've been doing, apart from this boy, and if he's got any sense in his head, he will stay well clear once you tell him that it's over with. You have to be strong, as he won't want to give up having sex with you, he's got something good going on, which is no strings sex. He will soon move on to somebody else, once he knows that there is no welcome between your legs. I don't know whether your marriage was arranged, or whether it was a last match, if it was arranged, and are not totally surprised if you had an affair. This is one of those issues that people know me for. I'm against a range marriages because it puts 2 people together who perhaps shouldn't be, with sometimes disastrous consequences. If you've ever had any love for your husband, try to think what it was that made you love him, and focus on that. A lot of women have affairs because their husbands either neglect them, all would never that or in bed in the 1st place. If that's the case, then it's up to you to enliven the sex between the 2 of you. If your husband was satisfying you in the 1st place, you probably wouldn't have got involved with somebody else. In no way is this a justification, but I can understand the lack of sexual fulfilment can push a woman into someone else's arms.
So, I'll say it again, forgive yourself!!! Once you can do that, life will be a lot easier for you.
The very best of luck to you, and remember, ditch the boyfriend, now!!!