How i can know when last time this person been on this site ? I can send e-mail and wait forever answer and never know this person been a month ago on this site

see her/his profile. It is written there when she/he last online

If they have ever posted to the forums, you can see the last
time they did:

You can click on the 'Posts #' beneath their forum picture.
Or, if you cannot find that:
http://mingle2.com/forum/show_posts_by_user/XXXXXXX

(Where the 'XXXXXXXs' represent the user-number.
If you know the user-name, you can right-click on
it anywhere (profile, forum, mail, etc.) which
renders a drop-down menu, select 'Properties' and
copy the URL (link shown)..the last digits of
which will be their user-number.

Place that number where the 'XXXXXXXs' are above.)
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Also, if they are in Stealth mode, their profile will NOT
show when last they were here.