+1 for Sipadan, however as Quero mentioned it might be a bit wet at that time of year, and if based on Mabul, the night life is restricted to a few post dive beers and an early night. Add to that a 4 hr flight to Semporna (from KL) + bus + boat, I'd be looking at somewhere easier with a better chance of decent weather. Quero's suggestion of Thailand is probably your best bet.
You did not mention where in India you will be visiting but I am thinking that you are traveling there via Malaysia hence the post. If that is the case, plenty of flights to Phuket from KL and much shorter than KL to Tawau then on to Mabul with about 3 more hours of travel.
On the other hand what are your key objectives, diving or night life?
I also travel frequently alone, never had any problems at any dive destination, even when they were quiet, despite the long travel times from KL to Mabul, that would be my first choice and if staying at Mabul, some really good shore diving too from the dive center's jetties as well as dive sites as close as 10 minutes by boat and of course the 40 min boat ride to Sipadan where most dive ops do 4 dives before returning to Mabul.