If the Tory cabinet supports TTIP then the veto will not be used.
If the Tory cabinet supports Brexit-TTIP it will happen if we leave.
Note you have completely failed to address my point about whether a trade deal requires the approval of the House of commons - you claim it does but you have provided no evidence whatsoever. I would consider this to be one of many government decisions that can be approved by the government alone, without reference to the commons. Certainly I cannot see how it would require primary legislation.
So lets look at the options then.
If the UK remains and the UK government doesn't want TTIP - it vetoes, result no TTIP.
If the UK remains and the UK government wants TTIP - it supports, but TTIP only happens if all other 27 support too. result, may get TTIP, may not.
If the UK leaves and the UK government doesn't want TTIP - it is in charge of the decision alone, result no TTIP.
If the UK leaves and the UK government wants TTIP - it is in charge of the decision alone, result TTIP.
So if you don't want TTIP and wouldn't want it even if this tory government wanted it, then you are much better in rather than out.