In Hinduism, it believes that marriage is a bonding for next 7 lives. Is that mean that he will not attain moksha at least in next 6 lives?
It's not true.
If one remains detached with own spouse & family, even while married, then that person is said to have knowledge & is eligible to attain self realisation.
BTW, "detached" doesn't mean "avoidance" of family. It should be interpreted as "not much excited".
BG 13.10-12 - Non-attachment and absence of fondness with regard to children, wives, homes, etc., and constant equanimity of the mind with regard to the attainment of the desirable and the undesirable; And unwavering devotion to 'Me' with single minded concentration; inclination to repair into a clean place; lack of delight in a crowd of people; Steadfastness in the knowledge of the Self, contemplation on the Goal of the knowledge of Reality --- these are spoken of as Knowledge. Ignorance is that which is other than this.
Note that in earlier times, polygamy was allowed. If "7 lives bond" was to be true then, the husband will keep taking incarnation after incarnation to finish each wife's 7. Hence it should be considered as a folklore. If it's true, even then marriage itself doesn't stop a person from attaining Moksha. e.g. Sri RAma, Drona, Krishna, ...
This folklore is mainly popular due to various movie songs. For example here it talks about 100 lives!