The syllables on their own are pronounced "gat'" and "i", but when put together the ㅌ links with the 이 and together become 치.
More of these pronunciation rules here: http://www.koreanwikiproject.com/wiki/Category:Consonant_assimilation (courtesy of a previous very helpful comment I've seen but can't remember where or by whom)
When the "i" vowel follows a consonant, the preceding consonant tends to change slightly: the middle of the tongue shifts toward the roof of the mouth (the hard palate) in preparation for the upcoming fronted high vowel (this process is called "palatalization"). This is why 시 sounds kind of like "she". This sound change happens with all the palatalized vowels in Korean (the ones with the double short stroke, like 여, 요, 예, etc).
There's another thing at work here, too: aspiration. ㅌ, ㅋ, ㅊ, and ㅍ are all aspirated consonants; they're pronounced with an extra puff of air. Since your tongue is already in place for the 이 after the 같 in 같이, that ㅌ turns into that aspirated, palatal consonant sound we usually associate with ㅊ.
I find it means "and" to show that the woman isnt the only subject here, which is why " 가", the ending subject particle, only comes after " 남자". To show that the woman AND the man are the subject. Instead of saying " 여자가 남자가" because that wouldㅇ be confusing: it is easier to put a subject particle on one thing than two and so 외 is used to show it is the woman AND the man. Im no expert, but that is how I have come to interpret it.
은/는 is the topic marker.
이/가 is the subject marker.
The former is mostly used for making general statements about the noun it's attached to. The latter is used for making a statement about a particular/specific example.
Ex: 사과는 과일 입니다. = "An apple a fruit." or "Apples are fruits."
사과가 맛없습니다. = The apple tastes bad.
No one reading this knows what answer you put in to explain what might've happened.
Although, you can use the "report" button and choose that your answer should've been accepted. It also has a option to add more details to the report. That said, the changes from a report on here seem to take a long time to happen. There aren't too many mods and I think they're doing it as volunteers.