filing for legal separation or annulment against a spouse with a 2nd family

Hi, good afternoon,

i guess it'll be better for me to present the facts first before asking my questions so here goes...

BACKGROUND:
- my husband (we were legally married last october 2000) and I have 3 kids, and are still currently married.

- sometime, 2007, he got his 18-year old (at that time) student pregnant, and has been keeping an on-off relationship with her ever since. however, they are not living together, and he claims that the kid was given the name of her mother in the birth certificate.

PRESENT SITUATION:
- my family are now geographically apart. my kids are in his province, he is working in the city where his mistress is residing, and i am working here in manila.

- the kids do not know of the situation yet.

- we see each other every 2 weeks when we would go home to visit the kids.

- i know that he has not yet let go of her, and i suspect that he has no plans to since it's already been 4 years.

- at the same time, we are also still together as husband and wife.

- i witness the inequality in the sense that, although my kids and i are bearing his name and are in his hometown staying with his parents, he does not give financial support and an equal share of his presence to my kids.

MY QUESTIONS:
1. is it true that i could file for a case against them that could put both of them behind bars? if yes, what case will that be? (just curious, since people always tell me that it is possible.)

2. does our situation qualify for an annulment case? if yes, are there pro bono services for this that we could avail of? if none, how much is the approximate price range for it? how many months will it take? also, what is the chance in percentage for it to be granted?

3. if i file for annulment, could we ask the court to order him to give regular financial support for my kids?

4. if an annulment is not feasible, could i file for legal separation? could i change my name back to my maiden name if this is granted? will he be mandated to give financial support for my kids? could he get married again? could i?

5. right now that we are still married, but i am the only one supporting my kids, could i file for my taxes as a single parent?

pardon the lengthiness of this post, i greatly need your help. i am only an ordinary working mom and can't afford the fees of a lawyer to answer these questions.

more power to you, and thank you in advance for your answers!

1) possible charge is concubinage, but you have to prove they are living together

2) i don't see a valid ground for annulment. grounds here: http://www.pinoylawyer.org/t4792-grounds-for-annulment-declaration-of-nullity-legal-separation-and-separatio-of-property

3)support can be part of an annulment case

4) you can change your name now if you want, but you can't compel the change of your records with govt agencies. legal sep will not allow you to remarry, but support can be granted.

5) it has no bearing whether you are single or not; but what you will need is a waiver on his part that he is not claiming the tax exemption of having children.